DESCRIPTION: (Scanned from the applicant's abstract) Recent studies have demonstrated that apoptosis is the underlying mechanism of germ cell death during normal spermatogenesis, and can be triggered by various physiological and pathological stimuli. The mechanisms by which these proapoptotic stimuli activate germ cell apoptosis are not well understood. The principal intracellular effectors of apoptosis are a family of cysteine proteases called caspases. These enzymes participate in a cascade involving initiator and executioner caspases that is triggered in response to proapoptotic signals. Active executioner caspases are then involved in the cleavage of key cellular proteins, resulting in eventual cell death. Four specific aims are proposed. Specific Aim 1 will focus on the characterization of the key molecular components of the intrinsic and extrinsic death pathways leading to caspase activation and increased germ cell apoptosis triggered by deprivation of the gonadotropic support or by mildly increased scrotal temperature. In Specific Aim 2, we will determine whether inhibition of germ cell apoptosis by replacement therapy of human FSH and/or LH, in the hormone deprivation model, will reverse the apoptosis related changes in the gene expression. Specific Aim 3 of this proposal will address the role of in vivo pre-treatments of rats with a broad-spectrum caspase inhibitor or a selective inhibitor of caspase 3 like proteases in preventing or attenuating the increased germ cell apoptosis induced by the hormonal and non-hormonal regulatory stimuli. Specific Aim 4 will focus on further characterization of the role of some of the key upstream modulators (p53, Bcl-2, Fas, and Fas L) of caspase activation in directing germ cell fate using mice harboring null mutation of either p53 or Bcl-2, or mice lacking functional Fas (lpr[cg]) or Fas L (gld). Results of these studies will provide insight into the basic control mechanisms of spermatogenesis in normal and pathological states and will be applicable to the assessment and management of male factor infertility as well as more targeted approaches to male contraception.